The stannides YbPtSn and Yb2Pt3Sn5

YbPtSn and Yb2Pt3Sn5 were prepared from the elements in sealed tantalum tubes in a high-frequency furnace in a novel water-cooled sample chamber. Both structures were refined from single-crystal X-ray data: YbPtSn (ZrNiAl type structure), space group P[unk]2m, a = 737.8(3) pm, c = 393.1(2) pm, wR2 = 0.0363, 412 F 2 values, 14 variables; Yb2Pt3Sn5 (new structure type), space group Pnma, a = 729.5(2) pm, b = 442.2(1) pm, c = 2625.2(6) pm, wR2 = 0.0373, 1378 F 2 values, 62 variables. The structure of YbPtSn contains two crystallographically different platinum positions. Both of them have tricapped trigonal prismatic coordination: [PtlSn6Yb3] and [Pt2Sn3Yb6]. Yb2Pt3Sn5 shows a close relation to the Y2Rh3Sn5 structure (space group Cmc21), however, with a different ordering of the platinum and tin atoms. Both ytterbium positions in Yb2Pt3Sn5 have the high coordination numbers (CN) of 20 for Yb1 and 18 for Yb2. Magnetic susceptibility measurements of Yb2Pt3Sn5 show Curie-Weiss behavior between 50 K and room temperature with an experimental magnetic moment of μ exp = 2.6(1) μ B/Yb, indicating mixed valency for the ytterbium atoms. Yb2Pt3Sn5 is a metallic conductor. 119Sn Mössbauer spectroscopic data show one signal at δ = 1.75(1) mm/s for YbPtSn and δ = 2.02(1) mm/s for Yb2Pt3Sn5. Both spectra are subjected to quadrupole splitting of ΔE q = 0.59(5) mm/s (YbPtSn) and ΔE q = 0.80(2) mm/s (Yb2Pt3Sn5).